ABSTRACT Chronic alcohol abuse and alcoholism are considered risk factors for prostate cancer (PCa) progression, but the mechanism is unknown. The current project will address an important question raised by clinicians: whether alcohol abstinence is an important therapeutic intervention in PCa. Previously, we found that: (1) fragmentation of the Golgi complex correlates with the progression of PCa; (2) ethanol (EtOH) induces Golgi disorganization that is caused by the impaired dimerization of the largest Golgi matrix protein giantin, which, in turn, alters intra-Golgi localization of some Golgi proteins. Indeed, we recently observed that in androgen-responsive PCa cells, EtOH- induced Golgi fragmentation leads to translocation of glycogen synthase kinase ? (GSK3?) from the Golgi to the cytoplasm, followed by the activation of HDAC6-HSP90-AR pathway. Additionally, we reported that non-muscle myosin IIA (NMIIA) motor protein forces EtOH-induced Golgi disruption. Also, alcohol induces endoplasmic reticulum (ER) stress and unfolded protein response (UPR), which are the known drivers of PCa advancement; however, the mechanism of EtOH-induced UPR in cancer remains largely uncovered. Here, we found that in low passage LNCaP cells, one of the UPR sensor, ATF6, is cleaved in Golgi by S1P and S2P proteases; however, EtOH treatment alters the Golgi localization of S1P and S2P, trapping them in the ER and facilitating ATF6 transactivation. Further, EtOH induces translocation of the glycosyltransferase MGAT3 from the Golgi to the cytoplasm followed by its degradation. However, MGAT5, the enzyme that competes with MGAT3 for N-glycan branching, is still retained in the Golgi. This results in MGAT5-mediated glycosylation of pro-metastatic proteins (including matriptase and integrins) and their overexpression at the cell surface. Finally, we detected that loss of NMIIA function prevents alcohol-induced Golgi fragmentation in PCa cells. This, in turn, recovers MGAT3?s intra- Golgi localization and reduces the expression of integrins. In light of these facts, we propose to test the hypothesis that alcohol accelerates PCa progression through Golgi fragmentation, which: (a) enhances ER stress response via induction of ATF6-mediated UPR, and (b) stimulates expression of pro-metastatic proteins over their abnormal MGAT5-mediated glycosylation. Hence, targeting alcohol-induced Golgi fragmentation is therapeutically important. The three specific aims of the proposed study are to: 1) elucidate the mechanism of alcohol-induced activation of ER stress by determining how alcohol metabolites induce translocation of Golgi localized S1P and S2P proteases to the ER; 2) examine the role of EtOH-induced MGAT5-mediated glycosylation in the progression of PCa; and 3) examine whether inhibition or knockdown of NMIIA prevents EtOH-induced Golgi fragmentation and attenuates the aggressive phenotype of PCa cells. The approach will include a variety of in vitro and in vivo experiments using EtOH-treated PCa cell lines, animal models and clinical samples from alcohol consuming PCa patients. The accomplishment of the goal of the proposed study would expand our understanding of the basic biology of PCa carcinogenesis, and elucidate the mechanisms of alcohol's tumor promotion action.